Where do deep-sea corals occur?

Unlike shallow coral species, which are restricted to the tropics and depend on symbiotic algae (zooxanthellae) to convert sunlight to food for much of their nutrition, deep-sea corals are found in all the world’s ocean basins, from coastal Antarctica to the Arctic Circle. While different species of deep-sea coral have different depth and temperature tolerances, they are azooxanthellate (lacking symbiotic algae) and generally occur at depths below 50 meters (m) (160 ft) and some species can occur at depths up to 6,000 m (20,000 ft) below the ocean’s surface.[a]

Several species of deep-sea corals form an underwater garden 165 m (540 ft) below the ocean’s surface off the coast of Alaska’s Aleutian Islands. Photo credit: Alberto Lindner/NOAA

Within U.S. waters, deep-sea coral communities have been identified in every region of the U.S. Exclusive Economic Zone (EEZ), an area extending 200 nautical miles (370 kilometers) offshore and covering 11.7 million square kilometers in the Pacific, Atlantic, and Arctic Oceans. Most deep-sea coral groups, with the exception of sea pens, occur on the scarce and scattered hard surfaces of the ocean floor, especially near the continental shelf break, along the continental slope, and on oceanic islands slopes and seamounts. [a,b]

Although we know that important deep-sea coral communities are found in all regions of U.S. waters except the Arctic (where only a few species have been reported), the majority of the U.S. EEZ has not been surveyed, mapped, or characterized. This makes it impossible to truly assess the overall extent of deep-sea coral communities. There is also very limited information on the organisms that live with these corals, how the organisms interact with or benefit from the deep-sea corals, or the degree to which individual deep-sea coral assemblages have been affected by human activities. Thus, we still have a lot to learn about these fascinating underwater communities.

This map shows where some of the most significant species of deep-sea corals are located.
Credit: NOAA NMFS (map); Ocean Biogeographic Information System (OBIS), accessed February 9, 2011 (data)